The present invention relates to a method for repairing interior portions of a pipeline having branch pipes such as a town gas pipeline or water pipeline. The qualities of pipes and of sealing device of a joint of the gas pipeline deteriorates with lapse of time, which causes leakage of gas from the pipeline Therefore, it is necessary to line the inner surface of an old pipeline with coating material such as resin.
A method of repairing the gas pipeline with pigs has been proposed. The method uses three pigs connected with each other by ropes at suitable distances, a first space between first and second pigs is filled with plastics having a low viscosity as a permeable material, and a second space between second and third pigs is filled with a puttying material The pigs are moved in the pipeline passing through a joint. During the movement of pigs, the plastics permeates into a sealing member such as a gasket in a space of the joint, and then the puttying material is charged in a space between adjacent pipes, substituting for the plastics in the space. Thus, the joint is sealed by the puttying material
In the method, the pig is caught at a joint where the diameter of the pipe changes, or at a bend, resulting in clogging of the pipeline and hence it becomes impossible to repair the pipeline. Therefore, the method can be used only under a very preferable condition.
In another method of repairing the pipeline, mist of resin is passed through a pipe line. In the method, only a resin having a low viscosity (for example, under 15,000 cps) can be employed, so that a thickness of a lining is small, at most, 0.5 mm. In addition, the lining on an upper inner surface of the pipeline is thinner than on a lower inner surface. Moreover, the lining becomes thin at an outer inner periphery of a bend where holes are most likely to be formed by corrosion. Accordingly, when resin having a permissively high viscosity is used to decrease the above-described drawbacks, a large amount of air under a pressure over 2 kg/cm.sup.2 must be supplied at a large flow rate. As a consequence, not only does a large lining device become necessary, but a large noise is generated so that the method is not suitable in a residential district. Furthermore, when an air pressure more than 2 kg/cm.sup.2 is applied to the pipeline, pinholes in the wall of the pipeline which are caused by corrosion are enlarged by the air blowing out therefrom, thereby causing the breaking of the pipe.